1. Field of the Invention
The present invention relates a scanning type charged particle beam microscope, such as a scanning electron microscope or a scanning ion microscope, and to a method of sampling a scanned image to a storing apparatus of the scanning type charged particle beam microscope.
2. Description of the Related Art
In a scanning type charged particle beam microscope, such as a scanning electron microscope or a scanning ion microscope, a secondary electron signal provided from a sample by a scanning signal is sampled to a storing apparatus in synchronism with the scanning signal to thereby constitute image data.
However, there is a delay of a signal in an electronic circuit and therefore, a scanning position of a charged particle beam and a storing position thereof to a storing apparatus are shifted from each other by an amount of delay time of the electronic circuit. Further, when the scanning speed is changed, there is a problem that at a fast scanning speed a storing position of a storing image is delayed in comparison to that at a slow scanning speed and a positional shift is produced in the image data. These problems exist because in the related art technology start of scanning and start of storing an image are carried out simultaneously with each other and, therefore, the scanning position and the storing position are shifted from each other by an amount of delay time of the electronic circuit. Further, the delay time of the electronic circuit is provided with a dispersion produced by a characteristic of an apparatus and, therefore, the delay time cannot be corrected uniquely.
In order to resolve the above-described problem, according to an aspect of the invention, when a timing signal such as a start signal of scanning is utilized as an image recording control signal, by delaying the signal by an amount of delay of an electronic circuit by using a shift register having a variable stage number, the delay of the electronic circuit is corrected to thereby prevent a positional shift of an image.
According to a scanning type charged particle beam microscope constituted as described above, a storing position is shifted from a scanning position by the amount of a delay time period of the electronic circuit and therefore, an operational position and the storing position coincide with each other. Further, when a stage number of the shift register having the variable stage number is adjusted while observing the image, delay time inherent to an apparatus can simply be adjusted.